Ethanol for industrial use is conventionally produced from petrochemical feed stocks, such as oil, natural gas, or coal, from feed stock intermediates, such as syngas, or from starchy materials or cellulose materials, such as corn or sugar cane. Conventional methods for producing ethanol from petrochemical feed stocks, as well as from cellulose materials, include the acid-catalyzed hydration of ethylene, methanol homologation, direct alcohol synthesis, and Fischer-Tropsch synthesis. Instability in petrochemical feed stock prices contributes to fluctuations in the cost of conventionally produced ethanol, making the need for alternative sources of ethanol production all the greater when feed stock prices rise. Starchy materials, as well as cellulose material, are converted to ethanol by fermentation. However, fermentation is typically used for consumer production of ethanol, which is suitable for fuels or human consumption. In addition, fermentation of starchy or cellulose materials competes with food sources and places restraints on the amount of ethanol that can be produced for industrial use.
Anhydrous ethanol is preferred for some applications, e.g., fuels. Anhydrous or substantially anhydrous ethanol, however, is often difficult to obtain from conventional hydrogenation and separation processes. Ethanol production via the reduction of alkanoic acids and/or other carbonyl group-containing compounds has been widely studied, and a variety of combinations of catalysts, supports, and operating conditions have been mentioned in the literature. During the reduction of alkanoic acid, e.g., acetic acid, other compounds are formed with ethanol or are formed in side reactions. These impurities limit the production and recovery of ethanol from such reaction mixtures. For example, the ethanol and water produced in conventional hydrogenation reactions may form a binary azeotrope. This azeotrope contains about 95% ethanol and about 5% water. Because the boiling point of this azeotrope (78° C.) is just slightly below that of pure ethanol (78.4° C.), an anhydrous or substantially anhydrous ethanol composition is difficult to obtain from a crude ethanol composition via simple, conventional distillation.
Therefore, a need remains for an improved process and system for the recovery of anhydrous ethanol composition from a crude product obtained by reducing alkanoic acids, such as acetic acid, and/or other carbonyl group-containing compounds.